Digestion & Absorption Of Lipids Flashcards

1
Q

What are the most common classes of lipids?

A

Triacylgylcerols/triglycerides
- 3 fatty acids bound to a glycerol backbone

Glycerophospholipid
- phospholipid that has a glycerol background

Sphingolipids

Steroids

Fatty acids

  • unsaturated = has double bonds
  • saturated = doesnt have double bonds
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2
Q

What fatty acids are essential?

A
Linoleic acid (18,2) 
- originates from omega-6

linolenic acid (18,3)

  • originates from omega-3
  • makes EPA and DHA byproducts

*are essential because they make arachidonic acid which are precursors for PGEs and leukotrienes

humans cannot synthesis fatty acids that contain cis-double bonds beyond position 9

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3
Q

What is arachidonic acid a precursor for?

A

Prostaglandins

Leukotrienes

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4
Q

Triacylglycerol functions

A

Primary storage form of energy and is the major macronutrient for lipids

Can be saturated or unsaturated/trans fats

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5
Q

Metabolic effects of each type of dietary fat

A

1) trans FA’s
- increases LDL and decreases HDL
- high levels increase CAD

2) saturated FA’s
- increases LDL with no effect on HDL

3) monounsaturated FA’s
- decreases LDL and slightly increases HDL
- decreases incidence of CAD

4) polyunsaturated omega-3 (linoleic acid)
- decreases LDL and HDL
- * produces arachidonic acid
- decreases risk of CAD

5) polyunsaturated omega-6 (DHA/EPA)
- no effect on LDL and HDL
- *most healthy one
- decreases incidence of CAD and SUD

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6
Q

What diseases are tied to high levels of lipids?

A

Heart disease

Malignant cancer

Stroke/ clotting issues

Diabetes

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7
Q

does dietary levels of cholesterol and fatty acids have a strong influence on plasma concentrations of each?

A

NO

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8
Q

What is the daily level of cholesterol produced by the liver?

A

1000mg

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9
Q

Classes of lipoproteins with associated apolipoproteins

A

1) HDL
- A-1/2 and E apolipoproteins
- ONLY has cholesteryl esters

2) LDL
- B100 apolipoproteins
- ONLY has cholesteryl esters

3) VLDL
- B100, E and C apoplipoproteins
- has more Triglycerides than cholesteryl esters

4) Chylomicrons
- A-1/4/5 and B48 apolipoproteins
- has wayyy more triglycerides than cholesteryl esters

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10
Q

What are phytosterols?

A

Mimic human cholesterol and signal the body to make less cholesterol
- also the body absorbs less cholesterol and empties it out

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11
Q

Emulsification

A

Process that occurs in the small intestine and requires bile
- prevents fat aggregation of cholesterol and triglycerides so that pancreatic lipase can do its job and break it down properly before it reaches the large intestine

Bile + TAGS/cholesterol = emulsion droplets
- emulsion droplets increase surface are for pancreatic lipase to function

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12
Q

What two complementary actions are done in emulsification?

A

Mechanical agitation

Secretion of bile salts

promote the production of increasingly smaller particles which increases the accessibility of lipids by pancreatic lipase in the small intestine

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13
Q

What is bile salts primary function?

A

Other than emulsification, stabilize small particles to prevent them from coalescing

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14
Q

What is the general overview of triacyglycerol digestion

A

1) TAGs enter body and the stomach
2) gallbladder releases bile salts and pancreas releases bicarbonate/pancreatic/coliapse lipase
3) combining from #2, TAGs -> emulsification droplets (single TAGs instead of multiple TAGs)
4) single TAGs are degraded by pancreatic lipase into Fatty acids + 2-monoacylglycerol (2-MG)
5) FAs + 2-MG -> micelles and nascent chylomicrons
6) nascent chylomicrons go back into blood stream via lymph and Bile salts/ collapse lipase go into ileum

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15
Q

What hormone causes the release of bicarbonate ions?

A

Secretin

  • releases in response to the low pH of chime
  • combats the low pH and provides appropriate pH for optimal pancreatic enzyme functions

Also CCK

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16
Q

What is the function of pancreatic lipase and colipase specifically?

A

both are released from the pancreas

Pancreatic:

  • esterase that cleaves FAs that are emulsified at carbon 1 and 3.
  • produces 2-MG and an FA from each TAG

Colipase:
- binds/anchors pancreatic lipase to promote enzymatic activity of pancreatic lipase

17
Q

Phospholipid digestion

A

Undergoes multiple rounds of digestion from 2 enzymes

1) phospholipase A2
- removes FAs from position 2 in a phospholipid
- produces lysophospholipid and a free FA

2) lysophospholipase
- removes FAs from position 1 from lysophospholipase
- produces glycerylphosphoryl base and a free FA

glyceralphosphoryl base gets recycled again through this mechanism or excreted via feeces

18
Q

What is the role of cholecystokinin (CCK)

A

Is a small peptide hormone that is released from mucosa cells of duodenum and jejunum
- is released only in response to presence of lipids and partially digested proteins

CCK = causes contraction of gallbladder and stimulation of exocrine cells of the pancreas. Also causes decreases in gastric motility
- causes release of bile and pancreatic enzymes

19
Q

What cells are lipids absorbed into the body by?

A

Enterocytes

20
Q

What is the fate of chylomicrons within the body after being produced in the small intestine?

A

1) renter the bloodstream via lymphatics
2) releases FA’s to muscles and adipose tissues
3) enters the liver and is uptaken by the liver, degreased by liver lysosomes
4) produces FA’s, cholesterol, AAs and glycerol byproducts

21
Q

What is the role of microsomes trigylceride transfer protein (MTP)?

A

Transfers lipids to apoB-48 as it is produced

Transfers lipid from cytoplasm to the ER lumen

ultimately blinds to apoB-48 particles and marks it for golgi secretion

22
Q

Abetalipoproteinemia

Bassein-Kornzweig syndrome

A

Defects in the MTP proteins
- results in a complete absence of Apo-B containing lipoproteins

Affects absorption of dietary fats/cholesterol and fat-soluble vitamins (DEAK)

Symptoms:

  • failure to thrive
  • diarrhea
  • star-shaped red blood cells
  • fatty stools
  • blindness/difficultly seeing
23
Q

What affects can sickle cell disease have on the GI tract?

A

Cholecystits

24
Q

How does orlistat cause weight loss?

A

Inhibits activity of pancreatic lipase
- reduces fat digestion and absorption

Works by forming a covalent bond with serine residues on gastric and pancreatic lipase

25
Q

Why are short chain and medium chained Triglycerides good for patients with steorrhea?

A

They dont require bile and pancreatic enzymes to break them down
- can be directly absorbed as is to the liver.

in steaorrhea, patients after have some sort of issue with pancreas/CCK/bile/etc. dysfunction